Microelectromechanical gyroscope with enhanced rejection of acceleration noises

ABSTRACT

An integrated microelectromechanical structure is provided with a driving mass, anchored to a substrate via elastic anchorage elements and designed to be actuated in a plane with a driving movement; and a first sensing mass and a second sensing mass, suspended within, and coupled to, the driving mass via respective elastic supporting elements so as to be fixed with respect thereto in said driving movement and to perform a respective detection movement in response to an angular velocity. In particular, the first and the second sensing masses are connected together via elastic coupling elements, configured to couple their modes of vibration.

BACKGROUND

1. Technical Field

The present disclosure relates to a microelectromechanical structure, inparticular a gyroscope sensitive to yaw angular accelerations, havingenhanced mechanical characteristics, in particular in the rejection ofacceleration noise.

2. Description of the Related Art

As is known, micromachining techniques enable manufacturing ofmicroelectromechanical structures or systems (MEMS) within layers ofsemiconductor material, which have been deposited (for example, a layerof polycrystalline silicon) or grown (for example, an epitaxial layer)on sacrificial layers, which are removed by chemical etching. Inertialsensors, accelerometers, and gyroscopes built using this technology arehaving a growing success, for example, in the automotive field, ininertial navigation, or in the sector of portable devices.

In particular, known to the art are integrated gyroscopes made ofsemiconductor material built using MEMS technology.

These gyroscopes operate on the basis of the theorem of relativeaccelerations, exploiting the Coriolis acceleration. When an angularvelocity is applied to a mobile mass that moves with a linear velocity,the mobile mass “feels” an apparent force, referred to as the “Coriolisforce”, which determines a displacement in a direction perpendicular toa direction of the linear velocity and to an axis about which theangular velocity is applied. The mobile mass is supported via springsthat enable its displacement in the direction of the apparent force. Onthe basis of Hooke's law, the displacement is proportional to theapparent force so that, from the displacement of the mobile mass, it ispossible to detect the Coriolis force and a value of the angularvelocity that has generated it. The displacement of the mobile mass can,for example, be detected capacitively, by determining, in resonanceconditions, capacitance variations caused by movement of mobileelectrodes, which are fixed with respect to the mobile mass and arecomb-fingered with fixed electrodes.

Published U.S. Patent Application Nos. US2007/0214883, US2009/0064780,and US2009/0100930, filed by the present applicant, disclose amicroelectromechanical integrated sensor with rotary driving movementand sensitive to yaw angular velocities.

The microelectromechanical sensor comprises a single driving mass,anchored to a substrate and actuated with rotary motion. Throughopenings are provided within the driving mass, and corresponding sensingmasses are set in the through openings; the sensing masses are enclosedwithin the overall dimensions of the driving mass, are suspended withrespect to the substrate, and are connected to the driving mass viaflexible elements. Each sensing mass is fixed with respect to thedriving mass during the rotary motion, and has a further degree offreedom of movement as a function of an external stress, in particular aCoriolis force, acting on the sensor. The flexible elements, thanks totheir particular construction, enable the sensing masses to perform alinear movement of detection in a radial direction belonging to theplane of the sensor, in response to a Coriolis acceleration. Thismovement of detection is substantially uncoupled from the actuationmovement of the driving mass. The microelectromechanical structure, inaddition to being compact (in so far as it envisages a single drivingmass enclosing in its overall dimensions a number of sensing masses),enables, with minor structural modifications, a uniaxial gyroscope, abiaxial gyroscope, or a triaxial gyroscope (and/or possibly anaccelerometer, according to the electrical connections implemented) tobe obtained, at the same time ensuring an excellent uncoupling of thedriving dynamics from the detection dynamics.

FIG. 1 shows an exemplary embodiment of a uniaxialmicroelectromechanical gyroscope, designated by 1, provided according tothe teachings contained in the aforesaid patent applications.

The gyroscope 1 is provided in a die 2, comprising a substrate 2 a madeof semiconductor material (for example, silicon), and a frame 2 b; theframe 2 b defines inside it an open region 2 c, which overlies thesubstrate 2 a and is designed to house detection structure of thegyroscope 1 (as described in detail hereinafter). The open region 2 chas a generally square or rectangular configuration in a horizontalplane (in what follows, plane of the sensor xy), defined by a firsthorizontal axis x and by a second horizontal axis y, which are fixedwith respect to the die 2; the frame 2 b has sides substantiallyparallel to the horizontal axes x, y. Die pads 2 d are arranged alongone side of the frame 2 b, aligned, for example, along the firsthorizontal axis x. In a way not illustrated, the die pads 2 d enable thedetection structure of the gyroscope 1 to be electrically contacted fromthe outside.

The gyroscope 1 comprises a driving structure, housed within the openregion 2 c and formed by a driving mass 3 and by a driving assembly 4.

The driving mass 3 has, for example, a generally circular geometry withradial symmetry, with a substantially planar configuration with mainextension in the plane of the sensor xy, and negligible dimension, withrespect to the main extension, in a direction parallel to a verticalaxis z, forming with the first and second horizontal axes x, y a set ofthree orthogonal axes, fixed with respect to the die 2. The driving mass3 defines at a central empty space 6, a center O of which coincides withthe centroid and a center of symmetry of the entire structure.

The driving mass 3 is anchored to the substrate 2 a by means of a firstanchorage 7 a set at the center O, to which it is connected throughfirst elastic anchorage elements 8 a. The driving mass 3 is possiblyanchored to the substrate 2 a by means of further anchorages (notillustrated), set outside the same driving mass 3, to which it isconnected by means of further elastic anchorage elements (notillustrated), for example, of the folded type. The first and furtherelastic anchorage elements enable a rotary movement of the driving mass3 about an axis of actuation passing through the center O, parallel tothe vertical axis z and perpendicular to the plane of the sensor xy,with a driving angular velocity {right arrow over (Ω)}_(a).

The driving mass 3 has a pair of through openings 9 a, 9 b, aligned in aradial direction, for example, along the second horizontal axis y, andset on opposite sides with respect to the empty space 6; the throughopenings 9 a, 9 b have in plan view a substantially rectangular shape,with main extension in a direction transverse to the radial direction.

The driving assembly 4 comprises a plurality of driven arms 10,extending externally from the driving mass 3 in a radial direction andarranged at equal angular distances apart, and a plurality of first andsecond driving arms 12 a, 12 b, extending parallel to, and on oppositesides of, respective driven arms 10. Each driven arm 10 carries aplurality of first electrodes 13, extending perpendicular to, and onboth sides of, the same driven arm 10. Furthermore, each of the firstand second driving arms 12 a, 12 b carries respective second electrodes14 a, 14 b, extending towards the respective driven arm 10, andcomb-fingered with the corresponding first electrodes 13.

The first driving arms 12 a are set all on one side of the respectivedriven arms 10, and are all biased at a first voltage; likewise, thesecond driving arms 12 b are all set on the opposite side of therespective driven arms 10, and are all biased at a second voltage. Adriving circuit (not illustrated) is connected to the second electrodes14 a, 14 b to apply the first and second voltages and determine, bymeans of mutual and alternating attraction of the electrodes, anoscillatory rotary motion of the driving mass 3 about the driving axis,at a given oscillation frequency and driving angular velocity {rightarrow over (Ω)}_(a).

The gyroscope 1 further comprises a pair of acceleration sensors withaxis parallel to the aforesaid radial direction, and in particular apair of sensing masses 15 a, 15 b housed within the through openings 9a, 9 b; the sensing masses 15 a, 15 b have, for example, a generallyrectangular shape with sides parallel to corresponding sides of thethrough openings 9 a, 9 b, are suspended with respect to the substrate 2a, and are connected to the driving mass 3 via elastic supportingelements 18. The elastic supporting elements 18 depart, for example,from the opposite major sides of each sensing mass in a radialdirection. In particular, the elastic supporting elements 18 are rigidwith respect to the motion of actuation of the driving mass 3 (in such away that the sensing masses 15 a, 15 b will follow the driving mass 3 inthe rotary movement), and also enable a linear movement of therespective sensing masses in the aforesaid radial direction.Furthermore, mobile electrodes 20 are coupled to the second sensingmasses 15 a, 15 b, extending, for example, from respective minor sides,in a direction orthogonal to the radial direction; the mobile electrodes20 form sensing capacitors with plane and parallel plates withrespective first and second fixed electrodes 22 a, 22 b, anchored to thedriving mass 3. In particular, each mobile electrode 20 forms a firstsensing capacitor C₁ with a respective first fixed electrode 22 a (forexample, the radially more internal one with respect to the center O),and a second sensing capacitor C₂ with a respective second fixedelectrode 22 b (for example, the radially more external one with respectto the center O).

In use, the gyroscope 1 is able to detect an angular velocity {rightarrow over (Ω)}_(z) (of yaw), acting about the vertical axis z. Inparticular, this angular velocity {right arrow over (Ω)}_(z) to bedetected generates a Coriolis force {right arrow over (F)}_(C) on thesensing masses 15 a, 15 b oriented in a radial direction (hence directedas a centripetal force acting on the same masses), causing displacementof the sensing masses and a capacitive variation of the correspondingsensing capacitors C₁, C₂. The value of the capacitive variation isproportional to the angular velocity {right arrow over (Ω)}_(z), whichcan thus be determined in a per-se known manner via a reading circuit,operating according to a differential scheme. In particular, appropriateconnections are provided between the fixed electrodes 22 a, 22 b and themobile electrodes 20 in such a way that the difference betweenelectrical quantities correlated to the variations of the first andsecond sensing capacitors C₁, C₂ are amplified in a differential way.

In particular, in the presence of the Coriolis force due to a yawangular acceleration acting on the structure, the sensing masses 15 a,15 b move in phase opposition in the radial direction (in other words,they displace in opposite senses, or orientations, with respect to theradial direction) so that the differential reading electronics generatesan amplified electrical output quantity. Instead, external accelerationsacting on the structure in the radial direction (for example,accelerations due to environmental noise) cause a movement in phase ofthe sensing masses 15 a, 15 b, which consequently is not read by thereading electronics (given that it does not cause an appreciableoutput).

Basically, the external accelerations are ideally rejected automaticallydue to the differential reading. In fact, whereas the useful Coriolissignal tends to unbalance the sensing masses 15 a, 15 b in oppositeradial directions, external accelerations determine variations with thesame sign (or sense). By means of the difference between the detectionsignals generated by the two acceleration sensors it is thus possible tomeasure the Coriolis contribution and reject the spurious accelerations.

The rotary driving motion also generates a centrifugal acceleration,which acts upon the sensing masses 15 a, 15 b, substantially in a waysimilar to the aforesaid Coriolis acceleration (i.e., causing adisplacement thereof in opposite directions). However, the centrifugalacceleration causes a contribution at output having a frequency that istwice that of the Coriolis acceleration, and can consequently beappropriately filtered by the reading electronics.

Even though the gyroscope described in the aforesaid patent applicationsrepresents a considerable improvement as compared to other structures ofa known type, it is not altogether optimized from the standpoint of theelectrical characteristics and noise immunity. In particular, in givenreal operating conditions, it is not perfectly immune to externalaccelerations (for example, noise accelerations), and also to theeffects of the centrifugal acceleration acting on the structure onaccount of the rotary driving motion.

BRIEF SUMMARY

The present disclosure provides a microelectromechanical gyroscopestructure having sensitivity to external acceleration noise and tocentrifugal acceleration. The gyroscope structure includes a drivingmass configured to be actuated in a plane with a driving movement; firstand second elastic anchorage elements anchoring the driving mass to asubstrate; and first and second elastic supporting elements. Thestructure also includes a first sensing mass and a second sensing masssuspended within said driving mass and respectively coupled to thedriving mass via the first and second elastic supporting elements,respectively. The sensing masses are configured to move with saiddriving mass in said driving movement and reconfigured to performrespective detection movements in response to an angular movement of thedriving mass. The structure further includes elastic coupling elementscoupling the sensing masses to each other and configured to couple modesof vibration of the sensing masses.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments are now described, purely by way of non-limiting example andwith reference to the attached drawings, wherein:

FIG. 1 shows a schematic top plan view of a microelectromechanicalgyroscope, of a known type;

FIG. 2 is a schematic representation of the elastic connections ofsensing masses of the gyroscope of FIG. 1;

FIGS. 3 a, 3 b and 4 a, 4 b show plots of electrical quantities in thegyroscope of FIG. 1;

FIG. 5 shows a schematic top plan view of a microelectromechanicalgyroscope according to a first embodiment of the present disclosure;

FIG. 6 is a schematic representation of the elastic connections ofsensing masses of the gyroscope of FIG. 5;

FIGS. 7 a, 7 b and 8 a, 8 b show plots of electrical quantitiescorresponding to the gyroscope of FIG. 5;

FIG. 9 shows a schematic top plan view of a second embodiment of themicroelectromechanical gyroscope;

FIGS. 10, 11 a, and 11 b show progressive enlargements of portions ofelements of the gyroscope of FIG. 9;

FIGS. 12 a and 12 b show plots of electrical quantities in the gyroscopeof FIG. 9;

FIG. 13 shows a further embodiment of the present disclosure,corresponding to a triaxial gyroscope; and

FIG. 14 shows a simplified block diagram of an electronic deviceprovided with a microelectromechanical gyroscope according to thepresent disclosure.

DETAILED DESCRIPTION

The present applicant has realized, and verified experimentally, thatnon-perfect immunity to external acceleration noise afflicting thepreviously described gyroscope can be attributed to possible processvariations (spread), and in particular to possible differences in themechanical characteristics of the sensing masses and of thecorresponding elastic elements, which can derive from this spread.

In detail, as shown in FIG. 2 (where the elastic connections between thesensing masses 15 a, 15 b and the driving mass 3 through the elasticsupporting elements 18 are represented schematically), the modes ofvibration of the sensing masses 15 a, 15 b are uncoupled from oneanother and ideally are at the same frequency.

Due to the process spread, the resonance frequencies of the two sensingmasses 15 a, 15 b may, however, not be perfectly coincident (forexample, they may differ from one another by 10-20 Hz), and this causes,for high factors of merit Q, a poor rejection to the externalacceleration noise. In fact, external accelerations having a frequencyclose to the resonance frequencies of the sensing masses 15 a, 15 b cangenerate responses considerably different in the two sensing masses,thus generating a non-zero output from the corresponding readingelectronics (even though the differential scheme adopted is ideally ableto reject these noises). Considering that the resonance frequency of thesensing masses has typical values in the region of 4-5 kHz, it isevident that also environmental noise with audio frequency can generate,for the reasons set forth above, even considerable output noises.

The above behavior has been verified by the present applicant by meansof appropriate numerical simulations. FIGS. 3 a and 3 b show the resultsof numerical processing in which a process spread was simulated byapplying a difference of 1% in the rigidity of the elastic supportingelements 18 associated to the sensing masses 15 a, 15 b, and a randomdisplacement noise of the anchorage 7 a (and of the possible furtheranchorages) of the driving mass was applied to simulate an externalacceleration excitation. In particular, FIGS. 3 a and 3 b show,respectively, in linear and logarithmic scale, the output OUT of thereading electronics of the gyroscope 1 (and thus the result of theoperations of amplification and demodulation of the signals at outputfrom the sensing capacitors), whilst FIGS. 4 a and 4 b show,respectively, the magnitude (Mag) and the phase of the mechanicaltransfer function of the sensing masses 15 a, 15 b. These graphshighlight the presence of two distinct frequency peaks set atapproximately 20 Hz apart, due to the different resonance frequencies ofthe two sensing masses 15 a, 15 b, and also the presence of a non-zerooutput from the reading electronics in the presence of noiseacceleration (which could have values that can even be comparable withthe values assumed during detection of angular accelerations).

To solve the aforesaid problems, one embodiment of the presentdisclosure envisages mechanical coupling (in particular via appropriateelastic elements) of the two sensing masses so as to couple theirdetection vibration modes.

In particular (reference may be made to FIG. 5, where the same referencenumbers are used for designating elements similar to others alreadydescribed previously), the microelectromechanical gyroscope, heredesignated by 30, differs from the gyroscope 1 of FIG. 1 substantiallyin that it comprises elastic coupling elements 32 a, 32 b designed tocouple the sensing masses 15 a, 15 b elastically to one another.

In this case, a single through opening is present, here designated by34, also coinciding with the empty space, here designated by 6′, definedat the center of the driving mass 3 (here having the shape of a circularframe). Located within the through opening 34 are both of the sensingmasses 15 a, 15 b, and the various elastic elements designed to ensurecoupling and mechanical support thereof via connection to the drivingmass 3.

In greater detail, the elastic coupling elements 32 a, 32 b areassociated with each sensing mass 15 a, 15 b, respectively; the elasticcoupling elements 32 a, 32 b depart, for example, from a major side ofthe respective sensing mass on an opposite side with respect to theelastic supporting elements 18 towards the center O (here just oneelastic supporting element 18 is present for each sensing mass). Theelastic coupling elements 32 a, 32 b are connected together via aconnection body 35, set in a central position, for example, at thecenter O. The connection body 35 is configured so as to havesubstantially negligible weight and dimensions, in particular ifcompared with those of the same sensing masses and of the elasticelements. As shown in the schematic representation of FIG. 6, theconnection body 35, in addition to being connected to the sensing masses15 a, 15 b, is connected to the driving mass 3 via further elasticsupporting elements 36. The further elastic supporting elements 36, forexample, constituted by springs of a folded type, extend, for example,in a direction transverse to the radial direction of alignment of thesensing masses 15 a, 15 b (coinciding with the direction of extension ofthe elastic coupling elements 32 a, 32 b), at the center O. Inparticular, the further elastic supporting elements 36 operate tofurther constrain the sensing structure to the driving mass 3, in orderto increase the rigidity of the sensing masses 15 a, 15 d with respectto translation along the vertical axis z.

In this case, the elastic anchorage elements of the driving mass 3 aremoreover arranged in a different way within the empty space 6′. Forexample, four anchorages 7 a ′ are provided, extending in pairs oneither side of the further elastic supporting elements 36, to which thedriving mass 3 is connected by means of respective elastic anchorageelements 8 a′, extending radially, in a way converging towards thecenter O.

The elastic coupling elements 32 a, 32 b have, in use, the function ofcoupling the movements of vibration of the sensing masses 15 a, 15 b,giving rise to two different separate vibration modes of the resultingmechanical sensing structure. In particular, a first vibration mode, inphase, and a second vibration mode, in phase opposition, are generated,having resonance frequencies that are clearly separate from one another.In both cases, the two sensing masses 15 a, 15 b vibrate at the samefrequency. It is consequently convenient, by the reading electronics(here appropriately modified), to reject the in-phase vibration modelinked to the noise accelerations, and preserve, for the subsequentprocessing operations, just the vibration mode in phase oppositionrepresenting the angular accelerations to be detected. In particular,noise rejection is principally associated to a differential typereading, where the in-phase vibration mode does not generate asignificant capacitive variation for the reading electronics.

FIGS. 7 a and 7 b show the results of a numerical processing similar tothe one previously described for the structure of a known type of FIG.1, directly comparing the values obtained with the gyroscope 30 of FIG.5 (represented with a solid line) and the values obtained with saidstructure of a known type (represented with a dashed line).

It may immediately be noted that coupling of the vibration modes of thesensing masses 15 a, 15 b generates at output (after appropriatedemodulation with respect to the driving frequency) two contributions ofnoise at frequencies clearly separate from one another: one,corresponding to the in-phase vibration, has a frequency that isapproximately twice that of the other, corresponding to the vibration inphase opposition. In particular, the frequencies of the twocontributions of noise are the result of a difference between thecorresponding resonance frequency (in phase, and in phase opposition)and the driving frequency.

Furthermore, it may immediately be noted that the aforesaid couplingenables a reduction in the output response of the gyroscope 30 to anexternal linear acceleration (for example, a noise acceleration) byapproximately one hundred times as compared to a traditional solution.

As is shown in FIGS. 8 a and 8 b, the mechanical system has a singlepeak, linked to the vibration mode in phase opposition, unlike solutionsof a known type, which are characterized by a double peak in frequency.

It is consequently clear that the described embodiment enables aconsiderable improvement of the rejection of the linear-accelerationnoises in the plane xy of the sensor. In particular, the frequencies ofthe two modes of vibration remain substantially unaltered in thepresence of process spread, and moreover the differential type readingenables convenient elimination of the undesirable contribution of thein-phase vibration mode.

From the mechanical standpoint, the aforesaid two different vibrationmodes derive from the different displacement modalities of the sensingmasses 15 a, 15 b, during the movement in phase or in phase opposition.In particular, during the movement in phase opposition, the displacementof the sensing masses 15 a, 15 b originates from the deformation both ofthe elastic coupling elements 32 a, 32 b and of the elastic supportingelements 18, so that the connection body 35 remains substantially stillin a central position. During the in-phase movement, the elasticcoupling elements 32 a, 32 b undergo a smaller deformation as comparedto the movement in phase opposition, the elastic supporting elements 36(which in the movement in phase opposition were substantiallystationary) are also deformed, and the connection body 35 displaces inthe radial direction.

The present applicant has, however, found that the gyroscope 30, albeitadvantageously enabling rejection of noise linear accelerations, is notaltogether free from problems due to the presence of the centrifugalacceleration. The rotation of the driving mass 3 generates in fact acentrifugal acceleration acting on the sensing masses 15 a, 15 b inopposite directions with respect to the radial direction of detection,and hence generates a vibration thereof in phase opposition (in a waysimilar to the effects of the Coriolis force linked to the yaw angularacceleration that is to be detected). As described in detail in theaforesaid patent application filed in the name of the present applicant,it may be shown that the centrifugal acceleration causes a contributionof vibration at a frequency that is twice that of the acceleration to bedetected so that ideally it is possible to filter its contribution.

However, the present applicant has verified that, in given operatingconditions, the centrifugal acceleration, notwithstanding the presenceof an adequate filtering stage, can cause a saturation of theamplification stages in the reading electronics, and thus cause in anycase errors in the detection of angular accelerations.

In order to solve this problem, a further embodiment of the presentdisclosure envisages automatic compensation, via an appropriategeometrical configuration of the sensing structure, of the effects ofthe centrifugal acceleration (i.e., providing an intrinsic mechanicalcompensation, as an alternative, or in addition, to a compensation madeat the reading electronics level).

As is shown in FIG. 9, a second embodiment of the gyroscope, heredesignated by 30′, differs from the one described previouslysubstantially for a different conformation of the mobile and fixedelectrodes, here designated by 20′ and, respectively, 22 a′, 22 b′, and,in the case illustrated, of the sensing masses, here designated by 15a′, 15 b′.

In particular, this second embodiment envisages a suitable shaping ofthe mobile electrodes 20′ and at least one between the respective firstor second fixed electrode 22 a′, 22 b′, in such a way as to generate,during the rotary driving motion, a capacitive variation of the sensingcapacitors able to compensate for a capacitive variation thereof due tothe presence of the centrifugal acceleration.

In detail, the sensing masses 15 a′, 15 b′ have in this case asubstantially trapezoidal conformation with a window 40 defined inside;mobile electrodes 20′ and the corresponding fixed electrodes 22 a′(radially more internal to the individual mobile electrode 20′) and 22b′ (radially more external to the individual mobile electrode 20′) arearranged within the window 40. The window 40 has, in the plane of thesensor xy, the shape of an annulus sector, and the mobile electrodes 20′and fixed electrodes 22 a′, 22 b′ are substantially arc-shaped.

The mobile electrodes 20′ extend inside the window 40, starting fromoblique sides of the respective sensing mass 15 a′, 15 b′. The first andsecond fixed electrodes 22 a′, 22 b′ associated to each mobile electrode20′ are set facing it on opposite sides, and are anchored to thesubstrate 2 a via respective anchorages 42 (see FIG. 10), which are alsoarranged within the window 40. In particular, two sets of mobileelectrodes 20′ and corresponding first and second fixed electrodes 22a′, 22 b′ are present, each set in a respective half into which theaforesaid window 40 is divided by the radial detection direction.

In greater detail, as illustrated in the progressive enlargements ofFIGS. 10, 11 a, and 11 b, each mobile electrode 20′ has a first lateralsurface (in particular the surface facing the respective first fixedelectrode 22 a′, or, equivalently, the lateral surface radially moreinternal with respect to the center O) that is shaped according to asuitable pattern, and a second lateral surface (in particular thesurface facing the respective second fixed electrode 22 b′, or,equivalently, the lateral surface radially more external with respect tothe center O) that is not shaped. In particular, the second lateralsurface that is not shaped corresponds to an arc of circumference,whilst the first lateral surface that is shaped has a undulate,substantially sinusoidal, profile (as highlighted by the top plan viewin the aforesaid FIGS. 10, 11 a, and 11 b).

Furthermore, whereas the second fixed electrode 22 b′ (radially moreexternal) has both of the lateral surfaces that are not shaped, thefirst fixed electrode 22 a′ (radially more internal) has both of thelateral surfaces shaped, in particular having one and the samesinusoidal profile, substantially corresponding to the sinusoidalprofile of the first lateral surface of the mobile electrode 20′.

In use, the centrifugal acceleration acting on each mobile mass 15 a′,15 b′, causes (as shown by the arrows) an undesired approach (in so faras it is not associated with the movement of detection of an angularacceleration) of each mobile electrode 20′ towards the correspondingsecond fixed electrode 22 b′, and a corresponding displacement of thesame mobile electrode 20′ away from the corresponding first fixedelectrode 22 a′, with a consequent decrease of capacitance of the firstsensing capacitor C₁, and an increase of capacitance of the secondsensing capacitor C₂ (the increase being greater, in a known way, thanthe aforesaid decrease, given the non-linearity of the relation betweencapacitance and distance between the electrodes). However, the movementof rotation of the driving mass 3 also causes a circumferentialdisplacement of the mobile electrode 20′ with respect to the fixedelectrodes 22 a′, 22 b′ (as shown by the arrows). Given the suitableshaping of the lateral surfaces of the electrodes constituting itsplates, this circumferential displacement causes a total capacitivevariation of the first sensing capacitor C₁ (in particular a capacitiveincrease thereof due to a net approach between the plates) such as toequal and compensate for the variations of the second sensing capacitorC₂ due to the contribution of the centrifugal acceleration. Furthermore,the frequency contribution of the capacitive variation due to theshaping of the electrodes substantially corresponds to the frequencycontribution due to the centrifugal acceleration (which, as indicatedpreviously, has a frequency that is twice the detection frequency) so asto enable an effective compensation for the resulting capacitivevariations. In other words, via the aforesaid shaping, it is possible togenerate a capacitive difference between the sensing capacitors (adifference that is then processed by the reading electronics), whichremains substantially constant in the absence of a Coriolis accelerationand thus of an angular acceleration to be detected.

Advantageously, also thanks to the fact that the value of capacitance ofthe second sensing capacitor C₂ is not affected by the circumferentialdisplacement of the mobile electrode 20′ due to the rotary drivingmotion, it is easy, via an appropriate mathematical model andappropriate computing algorithms, to determine the shaping parameters(in particular the parameters of the sinusoidal profile, in terms ofamplitude and/or period) that allows to obtain a minimization of thecapacitive difference ΔC between the sensing capacitors C₁, C₂ due tothe centrifugal acceleration. For example, an algorithm (of a knowntype, here not described in detail herein) of numeric integration of thecapacitive variations over the entire surface of the electrodes may beused for this purpose, to determine the parameters of the geometricalshape of the electrodes such as to minimize the capacitive differenceΔC.

In FIG. 12 a, the capacitive variation associated to the mobileelectrode 20′ during the driving motion on account of the solecentrifugal acceleration is represented with a solid line, and thecapacitive variation associated to the same mobile electrode 20′ causedby the sole shaping of the electrodes previously described isrepresented with a dashed line. As may be readily noted, the aforesaidcapacitive variations are substantially equivalent. Consequently, asillustrated in FIG. 12 b, the compensation error on the resultingcapacitive variation (capacitive difference ΔC, given by the differenceof the aforesaid capacitive variations) is, thanks to this intrinsicmechanical compensation, substantially zero or in any case negligible.In particular, it may be shown that this intrinsic compensation enablesreduction of the noise effect of the centrifugal acceleration by afactor equal to 100.

Although it is clear, it is emphasized that the sinusoidal shapedescribed previously is not the only shape possible to obtain theaforesaid effect, and that other geometrical shapes are equallypossible, the parameters of which may again be determined via numericalgorithms (for example, there may be envisaged a shaping with asaw-tooth profile).

A further embodiment of the present disclosure envisages provision of abiaxial or triaxial gyroscope by adding to the previously describeddetection structure for sensing yaw angular accelerations, a detectionstructure for sensing pitch and/or roll angular accelerations,substantially as described in the aforesaid patent applications filed inthe name of the present applicant.

An example of a triaxial gyroscope thus obtained is shown in FIG. 13,where it is designated by the reference number 30″.

In brief (but reference may be made to the aforesaid patent applicationsfor further details), the gyroscope 30″ (illustrated schematically) inthis case comprises a first pair and a second pair of further sensingmasses 46 a-46 b and 46 c-46 d, housed within respective throughopenings in the driving mass 3 and connected thereto via respectiveelastic elements 47.

The further sensing masses 46 a, 46 b of the first pair are aligned in afirst diametric direction x₁, inclined with respect to the firsthorizontal axis x of the die 2 by an angle of inclination α (consideredin a counterclockwise direction), the value of which is comprisedbetween 40° and 50° and preferably is 45°. Likewise, the further sensingmasses 46 c, 46 d of the second pair are aligned in a second diametricdirection x₂, substantially orthogonal to the first diametric directionx₁, and inclined with respect to the first horizontal axis x by the sameangle of inclination α (considered in this case in an oppositedirection, i.e., clockwise). Furthermore, the further sensing masses 46a, 46 b of the first pair are symmetrical to corresponding furthersensing masses 46 d, 46 c of the second pair, with respect to an axis ofsymmetry of the die pads 2 d (coinciding with the second horizontal axisy). For example, the further sensing masses 46 a-46 d are, in plan view,substantially shaped like a radial annulus sector, and constituteacceleration sensors with axis parallel to the vertical axis z. In use,an angular acceleration of pitch or roll generates a Coriolis force onthe further sensing masses 46 a-46 d such as to cause a rotation thereofout of the plane of the sensor xy, and an approach towards (or a movingaway from) respective detection electrodes facing them and set on thesubstrate 2 a (represented with a dashed line).

Further anchorages 7 b are also shown in FIG. 13, which are set outsidethe driving mass 3; the driving mass is anchored to the substrate 2 avia these further anchorages 7 b, to which it is connected by means offurther elastic anchorage elements 8 b.

FIG. 14 illustrates an electronic device 50 comprising themicroelectromechanical gyroscope 30′ (or 30″) previously described. Theelectronic device 50 can advantageously be used in a plurality ofelectronic systems, for example, in inertial navigation systems, inautomotive systems or in systems of a portable type, such as, forexample: a personal digital assistant (PDA); a portable computer; a cellphone; a digital audio player; a photographic camera or video-camera; orfurther systems capable of processing, storing, transmitting, andreceiving signals and information.

The electronic device 50 further comprises: a driving circuit 51,operatively coupled to the driving assembly 4 for imparting the rotarydriving movement on the driving mass 3 and supplying biasing signals tothe microelectromechanical structures (in a per-se known manner, herenot illustrated in detail); a reading circuit 52, operatively coupled tothe sensing capacitors C₁, C₂ of the sensing masses, for detecting theamount of displacement of the sensing masses and hence determining theangular velocity acting upon the structure; and an electronic controlunit 54, for example, of a microprocessor type, connected to the readingcircuit 52, and designed to supervise the general operation of theelectronic device 50, for example, on the basis of the angularvelocities detected and determined.

The advantages of the microelectromechanical gyroscope providedaccording to the present disclosure are clear from the foregoingdescription.

In particular, it is again emphasized that mechanical coupling viaelastic elements of the sensing masses for detecting yaw angularaccelerations enables rejection of external acceleration noise (forexample, due to environmental noise or other source of noise), even inthe presence of process spread.

The particular shaping pattern of the detection electrodes enablescompensation and minimization of the effects of the centrifugalacceleration due to the rotary driving movement. In particular, theseeffects are intrinsically compensated for without requiring anyparticular additional arrangements within the reading electronics.

Furthermore, the detection structure for detecting yaw accelerations hasan architecture that is altogether compatible with a biaxial or triaxialgyroscope, enabling its integration with structures for detecting pitchand/or roll angular accelerations.

Finally, it is clear that modifications and variations may be made towhat has been described and illustrated herein, without therebydeparting from the scope of the present disclosure.

In particular, it is clear that modifications can be envisaged to theconfiguration of some of the structural elements of the gyroscope. Forexample, the sensing masses 15 a″, 15 b″ for detection of yaw angularaccelerations can be aligned in a different direction in the plane ofthe sensor xy (for example, along the first horizontal axis x); adifferent conformation of the elastic coupling elements 32 a, 32 b andof the connection body 35 may be envisaged; it is possible to shapeaccording to a desired pattern both the first and the second fixedelectrodes 22 a′, 22 b′, or else it is possible to shape only theradially-more-external second fixed electrodes 22 b′; both the first andthe second fixed electrodes 22 a′, 22 b′ can possibly extend on theoutside of the corresponding sensing masses 15 a″, 15 b′, in a waysubstantially similar to what is illustrated with reference to FIG. 5.More in general, the driving mass 3 may have a different shape,different from the circular one, such as a closed generically polygonalshape, as likewise the shape of the frame 2 b of the die 2 may bedifferent.

Furthermore, the displacement of the sensing masses can be determinedwith techniques different from the capacitive one, for example, by meansof detection of a magnetic force, and the twisting moment for causingoscillation of the driving mass with rotary movement can be generated ina different way, for example, by means of parallel-plate electrodes, orelse by magnetic actuation.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A microelectromechanical structure,comprising: a substrate; a driving assembly having a first set ofdriving electrodes and a second set of driving electrodes; elasticanchorage elements anchoring portions of the driving assembly to thesubstrate; first and second elastic supporting elements; a first sensingmass and a second sensing mass positioned between the first and secondset of driving electrodes, the first sensing mass coupled to the drivingassembly via the first elastic supporting element and the second sensingmass coupled to the driving assembly via the second elastic supportingelement, the first and second sensing masses being configured to bemoved by the driving assembly and configured to move in response torotation of the microelectromechanical structure; a rigid connection barpositioned between the first sensing mass and the second sensing mass;first and second elastic coupling elements coupled between the first andsecond sensing masses and the connection bar, respectively, the elasticcoupling elements configured to couple movement of the first and secondsensing masses together to move at substantially the same frequency; anda third sensing mass and a fourth sensing mass positioned between thefirst and second set of driving electrodes, the first and second sensingmasses being aligned along a first axis and the third and fourth sensingmasses being aligned along a second axis that is angled with respect tothe first axis by less than 90 degrees, the third and fourth sensingmasses being movably coupled to the driving assembly without beingmoveably coupled to the connection bar.
 2. The structure of claim 1wherein the driving assembly is configured to drive with a rotarymotion.
 3. The structure of claim 1 wherein the driving assemblyincludes a single driving mass having a rectangular opening along areference axis, the first and second sensing masses being positionedwithin the rectangular opening.
 4. The structure of claim 3 wherein thedriving mass includes four additional openings that are arranged atangles from the reference axis where the angles are less than 90degrees.
 5. The structure of claim 4 wherein two of the four openingsare separated from the other two openings by the rectangular opening. 6.The structure of claim 4 wherein the four additional openings arenon-rectangular.
 7. The structure of claim 1 wherein the connection barhas a first side and a second side that are each longer than a thirdside and a fourth side, the first elastic coupling element being coupledto the first side of the connection bar and the second elastic couplingelement being coupled to the second side of the connection bar.
 8. Thestructure of claim 7 wherein the connection bar is coupled to a drivingmass with a third elastic coupling element.
 9. The structure of claim 8wherein the connection bar is coupled to the driving mass with a fourthelastic coupling element, the third elastic coupling element beingcoupled to the first side of the connection bar and the fourth elasticcoupling element being coupled to the second side of the connection bar.10. A gyroscope, comprising: a substrate having a first reference axisand a second reference axis that is perpendicular to the first referenceaxis; a driving assembly coupled to the substrate and having a first setof driving electrodes and a second set of driving electrodes; aplurality of moveable masses coupled to the driving assembly andpositioned between the first and second set of driving electrodes, afirst pair of the plurality of moveable masses, each having a center ofmass along a third axis that is between the first reference axis andsecond reference axis, a second pair of the plurality of moveablemasses, each having a center of mass along the first reference axis, thefirst pair of movable masses being configured to detect rotation aboutthe first reference axis and the second reference axis; and a couplingelement coupled between the second pair of the plurality of moveablemasses to couple movement of the second pair of movable masses togetherwithout coupling the movement of the first pair of movable masses. 11.The gyroscope of claim 10 wherein the plurality of moveable masseincludes a third pair of moveable masses, each having a center of massalong a fourth axis that is perpendicular to the third axis.
 12. Thegyroscope of claim 10 wherein the second pair of the plurality ofmoveable masses are configured to move together at substantially thesame frequency.
 13. A device, comprising: a substrate; a drivingassembly having a plurality of driving electrodes; a first moveable masspositioned between at least some of the plurality of driving electrodes,the first moveable mass being configured to be moved by the drivingassembly and configured to move in response to an angular rotation ofthe device; a second moveable mass positioned between at least some ofthe plurality of driving electrodes, the second moveable mass beingconfigured to be moved by the driving assembly and configured to move inresponse to an angular rotation of the device; and first and secondelastic springs; rigid coupling bar that is coupled between the firstand second moveable masses, the coupling bar configured to cause thefirst and second moveable masses to be moved by the driving assembly atsubstantially the same frequency, the first elastic spring coupledbetween the coupling bar and the first mass and the second elasticspring coupled between the coupling bar and the second mass; and a pairof third movable masses aligned with each other and positioned along afirst axis, the first and second movable masses being aligned with eachother and positioned along a second axis that is angled with respect tothe first axis, the pair of third movable masses being moveably coupledto the driving assembly without being moveably coupled to the couplingbar such that the pair of third movable masses are configured to movewithout constraint by the coupling bar.
 14. The device of claim 13,further comprising a third elastic spring and a fourth elastic springeach coupled between the coupling bar and the driving assembly.
 15. Thedevice of claim 14 wherein the third and fourth elastic springs arefolded springs.
 16. The device of claim 13 wherein the driving assemblyis configured to drive with a rotary motion.
 17. The device of claim 13wherein the driving assembly includes a single driving mass, the firstand second sensing masses being positioned within the driving mass. 18.The device of claim 17 wherein the driving mass is round.
 19. The deviceof claim 17 wherein the coupling bar is coupled to the driving mass withthird and fourth elastic springs.
 20. The device of claim 13 whereineach mass of the pair of third movable masses is physically separatefrom the other mass of the pair of third movable masses.
 21. A device,comprising: a substrate having a first reference axis and a secondreference axis that is perpendicular to the first reference axis; afirst pair of moveable masses located above the substrate, each having acenter of mass along a third axis that is between the first referenceaxis and second reference axis; a second pair of moveable masses locatedabove the substrate, each having a center of mass along the firstreference axis; a driving assembly elastically coupled to the first andsecond pairs of moveable masses and configured to drive the first andsecond pairs of moveable masses; and a coupling bar coupled between thesecond pair of moveable masses to couple movement of the second pair ofmovable masses together without coupling the first pair of movablemasses to the coupling bar.
 22. The device of claim 21 wherein the firstpair of movable masses is configured to detect rotation about the firstreference axis and the second reference axis.
 23. The device of claim 21wherein the second pair of movable masses is configured to detectrotation about a fourth axis that is perpendicular to the first andsecond reference axis.